The present invention relates to an indexing device used for a machine tool, and particularly to an indexing device including a rotary unit rotatably supported on a base, and a plurality of engaging elements provided between the rotary unit and the base, the engaging elements being relatively movable between an engaged position at which the rotary unit is fixedly held at respective indexed positions on the base and a disengaged position at which the rotary unit is permitted to be rotationally indexed. The present invention may be applied, for example, to a turret tool rest provided for an automatically operated lathe. However, this is not exclusive and other applications are also allowed.
In a field of machine tools, an indexing device is used for locating a tool or a workpiece at predetermined positions for the purpose of automating the machining operation, increasing the machining speed as well as providing for multi-kind production of a small number of items. As this type of the indexing device, a turret tool rest for selecting a desired tool from a number of tools previously mounted thereon at regular intervals in a circumferential direction and locating the same at a predetermined working position, an index table for locating a desired objective surface to be machined of a workpiece at a predetermined working position to allow automatic multiple-surface machining of the workpiece, and so on, have been known.
The turret tool rest used for an automatically operated lathe, which is one rotary type indexing device, has a structure wherein a turret, as a rotary unit mounted on a base, rotates to automatically index a plurality of (usually five to twelve) indexed positions. A plurality of tool mounting portions are formed on an outer circumferential or axial end surface of the turret in correspondence to the indexed positions various tools including a cutting tool, a drill, etc., can be mounted onto the tool mounting portions. One of these tools suitable for the desired machining operation is automatically selected and located at a predetermined working position on the automatic lathe by the indexing rotation of the turret. In this regard, the term xe2x80x9caxial directionxe2x80x9d used in this text stands for the direction along a rotation axis or a central axis of an object.
While the workpiece is cut or drilled by the selected tool in the turret tool rest, it is necessary to firmly secure the turret on the base at the indexed position. In most cases, even in other indexing devices, it is required to firmly secure the rotary unit at the indexed position. Accordingly, a plurality of engaging elements are generally provided between the base and the rotary unit, which can be mutually engaged and disengaged (that is, a clamping and unclamping operation). By the mutual engagement or disengagement of these engaging elements, the rotary unit is made free, to be rotationally indexed, or is securely located at a predetermined indexed position.
In the field of conventional turret tool rests, a coupling unit comprising a pair of crown gear-shaped coupling elements, each having a number of teeth on one axial end face thereof, and adapted to be intermeshed with each other (this is called, for example, a curvic coupling) is used.
In this type of engaging unit, the engagement/disengagement is generally carried out by linearly displacing one engaging element (or rotating teeth) provided on the rotary unit in the axial direction relative to the other engaging element (or stationary teeth) provided on the base. Accordingly, when the rotary unit is to be rotationally indexed, the engaging element on the rotary unit is displaced in the axial direction from the engaged position, at which the engaging elements are engaged with each other, so as to release the engagement between the engaging elements (an unclamping operation), and the rotary unit is rotationally indexed at a disengaged position at which the engaging elements are completely disengaged from each other. After the indexing operation, the engaging element on the rotary unit is displaced again in the axial direction so as to engage the engaging elements with each other (a clamping operation), whereby the rotary unit is fixedly secured at the indexed position.
Generally, in the pair of engaging elements with the above structure, mutually opposed teeth in the axial direction have circumferentially opposite, slanted lateral faces for facilitating the mutual engagement/disengagement by the axial movement. In this case, until the engaging elements are completely engaged, i.e., the slanted lateral faces of the opposed teeth closely contact with each other, a gap is inevitably defined between the slanted lateral faces of the teeth, whereby the engaging elements cannot be fixedly secured to each other. Thus, a positional displacement may be generated in a rotational direction between the engaging elements within a rotational angle until the teeth are abutted to each other, which may allow the rotary unit to freely rotate on the base.
In the turret tool rest, for example, when a weight imbalance exists in the rotary unit relative to the rotation axis, due to, e.g., the deviated arrangement of tools in the tool mounting portions in the turret, the abovesaid free rotation of the turret is liable to occur due to the gap formed between the slanted lateral faces of the opposed teeth, before the pair of coupling elements are completely engaged.
Also, in general, the indexing device is adapted so that the rotary unit is operatively coupled to a rotationally indexing drive source, so as to be capable of receiving a driving force from the drive source, when the engaging elements are completely disengaged from each other to allow the relative rotation. It will be understood, in view of the above, that there might be a possibility of relative positional displacement in the rotational direction even if the teeth of the engaging elements have lateral faces parallel to the axis, instead of the slanted lateral faces as mentioned above, immediately after the engaging elements have been disengaged from each other.
If such a positional displacement in a rotating direction repeatedly occurs every time the engaging elements mutually engage or disengage, there might be a risk of wear or breakage of a number of teeth of the engaging elements due to the relative sliding or collision therebetween. Because the engaging elements must have a highly accurate positioning function for performing the precise rotational indexing, it is required that positional displacement in the rotational direction should be prevented as much as possible.
An object of the present invention is to provide an indexing device comprising a rotary unit and a plurality of engaging elements for fixedly supporting the rotary unit at indexed positions, which can prevent the engaging elements from shifting in the rotational direction to each other while they are moving between a mutually engaged position and a mutually disengaged position until the mutual engagement has completed, whereby wear and breakage of the engaging elements are effectively avoidable.
To achieve the above object, the present invention provides an indexing device comprising a base; a rotary unit movably supported on the base; at least two engaging elements provided in respective association with the base and the rotary unit and engageable with each other; drive means for rotationally indexing the rotary unit on the base, and for moving the at least two engaging elements between an engaged position at which the at least two engaging elements are engaged with each other to fixedly hold the rotary unit at respective indexed positions on the base and a disengaged position at which the elements are disengaged from each other to enable the rotary unit to be rotationally indexed; and rotation inhibiting means for inhibiting the rotary unit from freely rotating on the base during a moving operation of the at least two engaging elements between the engaged position and the disengaged position.
In a preferred aspect, the rotation inhibiting means comprises at least one movable projection retractably provided on the rotary unit, at least one engaging portion fixedly provided on the base to be engaged with the movable projection when the rotary unit is located at the indexed position, and biasing means for biasing the movable projection in a direction for maintaining an engagement of the movable projection with the engaging portion.
In this arrangement, it is advantageous that the movable projection includes an outwardly convexly curved end surface, and that the engaging portion comprises a countersink provided on a surface of the base so as to receive the end surface of the movable projection.
Also, it is desirable that the movable projection comprises a plunger axially slidably supported in a sleeve provided in the rotary unit.
Preferably, the biasing means comprises a spring.
Advantageously, the rotation inhibiting means further comprises a friction member provided between the base and the rotary unit.
In another preferred aspect, the at least two engaging elements comprise a plurality of stationary teeth fixedly provided on the base and a plurality of rotary teeth fixedly provided on the rotary unit, and the drive means linearly moves the rotary unit along a rotation axis of the rotary unit on the base, so as to move the stationary teeth and the rotary teeth between the engaged position and the disengaged position.
In this arrangement, it is advantageous that the stationary teeth and the rotary teeth have respective slanted lateral faces capable of being closely contacted with each other, and that the rotation inhibiting means inhibits the rotary unit from freely rotating on the base during the moving operation of the stationary teeth and the rotary teeth between the engaged position at which the slanted lateral faces of the stationary teeth and the rotary teeth are closely contacted with each other and the disengaged position at which the slanted lateral faces are disengaged from each other to an extent allowing rotation of the rotary teeth without interfering with the stationary teeth.
Also, it is preferred that the rotation inhibiting means comprises at least one plunger axially slidably supported in a sleeve provided in the rotary unit and including an outwardly convexly curved axial end surface, at least one countersink provided securely on a surface of said base to receive the axial end surface of the plunger when the rotary unit is located at the indexed position, and a spring for biasing the plunger in a direction for maintaining an engagement of the axial end surface of the plunger with the countersink.
Further, the present invention provides a turret tool rest comprising a base; a turret movably supported on the base, on which desired tools, including a rotating tool, can be mounted at predetermined indexable angled positions; a first servo motor for driving the rotating tool; a pair of clutch pieces, one of which is operatively connected to the first servo motor and the other of which is operatively connected to the turret; a pair of coupling elements provided in respective association with the base and the turret and engageable with each other; a second servo motor for moving the pair of clutch pieces between an operative position at which the clutch pieces are engaged with each other and transmit a driving force of the first servo motor to the turret so as to rotationally index the turret and a nonoperative position at which they are disengaged from each other so as to separate the turret from the first servo motor, and for moving the pair of coupling elements between an engaged position at which the coupling elements are engaged with each other and hold the turret in respective indexed positions on the base and a disengaged position at which they are disengaged from each other to permit the turret to be rotationally indexed; an interlocking mechanism for interlocking the clutch piece with the coupling element in operation, so that the pair of coupling elements move to the engaged position when the pair of clutch pieces move to the non-operative position, and the pair of coupling elements move to the disengaged position when the pair of clutch pieces move to the operative position; and rotation inhibiting means for inhibiting the turret from freely rotating on the base during moving operations of the pair of clutch pieces between the non-operative position and the operative position and simultaneously of the pair of coupling elements between the engaged position and the disengaged position; wherein the rotation inhibiting means comprises at least one movable projection retractably provided on the turret, at least one engaging portion fixedly provided on the base to be engaged with the movable projection when the turret is located at the indexed position, and biasing means for biasing the movable projection in a direction for maintaining an engagement of the movable projection with the engaging portion.